Many peptides with unique structural features display distinct biological properties. The studies of this project were aimed at the analysis and synthesis of molecules with rarely encountered amino acids. Of foremost concern were: (a) the synthesis of precursors of ring A of nisin, a peptide with alpha,beta unsaturated and thioether amino acids; (b) the action of peptide structures based on nisin and/or the linear gramicidins on neonatal and neoplastic tissue; (c) the synthesis of analogs of the gramicidins A, B, and C, and the correlation of their structures with ion-transport across lipid bilayers; (d) the synthesis of peptides with agonistic and antagonistic effects of fertility regulating hormones inclusive of the large-scale preparation of the luteinizing hormone releasing factor (LRF) for clinical purposes; (e) the exploration of dehydroalanine resins for the synthesis of peptide amides; (f) the synthesis of analogs of opioid peptides with agonist and/or antagonist properties; (g) the synthesis of analogs of a pentapeptide with chemotactic characteristics; (h) the structural investigation of the heterodetic pentacyclic peptide CINNAMYCIN and DURAMYCIN; (i) the development of new techniques for peptide synthesis, amino acid analysis, and the nonenzymatic cleavage of the peptide bond.